The present invention relates to dropper tips and containers for dispensing of selected liquids in drop form, and, more particularly, to dropper tips, containers, and closures for dispensing liquids in drop form in less than 60 microliter volumes with precise first-drop volumes and minimum drop-to-drop volume variations.
The common dropper tip used in laboratory-type "squeeze" bottles and dispensers is typically formed from a rigid or resilient material, such as glass, plastic, or metal, and has an elongated hollow stem that terminates in a nozzle-like tip through which the liquid to be dispensed flows. Typically, the base of the dropper tip, that is, the end that is attached to the liquid-carrying container, is formed with a fitment that is pressed into or otherwise inserted into the neck portion of the plastic squeeze bottle. The squeeze bottle is typically inverted by the user and manually squeezed to dispense one or more drops through the hollow stem. In the general area of chemical and biological analysis, a number of disposable test kits have been developed that include prepackaged chemicals, reagents, and other fluids that are used to effect analysis or other tests involving the drop-wise dispensing of a fluid. When the various liquids are fully dispensed, the components of the kit are discarded. Disposable test kits represent an inexpensive and convenient manner by which tests may be effected without the need for traditional re-usable laboratory equipment. In some cases, the cost of the chemicals involved is quite high, and, in order to provide an economically feasible and disposable test kit, small volumes (i.e., 3 to 7 milliliters) of the fluid are provided in resilient plastic squeeze bottles for use by the user with volumetrically small drops dispensed from the tips, these drops typically being less than 60 microliters and often in the 12 to 50 microliter range. Where it is important to dispense precise first-drop volumes and precise second and subsequent drop volumes, any significant drop-to-drop variations in the drop volume can affect the test results, i.e., a drop-to-drop volumetric variation above a predetermined limit can cause an undesired oversupply or undersupply of the dispensed fluid.
The traditional resilient squeeze bottle has been found to have a substantial drop-to-drop volumetric variation when dispensing one or more drops under 60 microliters and particularly drops in the 12 to 50 microliter range. For example, when a squeeze bottle is initially inverted, the headspace gas in the neck portion of the bottle normally rises to the top of the liquid in the now inverted bottle. Oftentimes, one or more bubbles of the headspace gas may adhere to a surface at or adjacent the entry opening of the dropper stem. Also, it has been observed that a single headspace bubble will occupy the entire neck region of the bottle and prevent the liquid from readily entering the dispenser stem. The typical user has an empirical expectation that a first drop will be dispensed upon the application of an initial squeezing force. When one or more headspace-gas bubbles are present, the bubbles may enter the lumen of the dispensing stem to interfere with the flow of liquid through the lumen and prevent the formation of the first drop in a manner consistent with the user's expectation. In this instance, the normal response of the user is to incrementally increase the squeezing force in an attempt to drive liquid to the end of the dispensing tip to form a drop. Where the second increment of squeezing force does not produce a drop, it has been observed that most users will dramatically increase the squeezing force in an attempt to dispense a drop. Usually, this third increment of increased squeezing force is successful in expelling the entrained air in the lumen and also forces enough liquid to the end of the dropper tip to generate an unintended succession of drops. When the squeezing force is relaxed after one or more drops are dispensed, air will be aspirated through the lumen into the inverted bottle and oftentimes forms a bubble that adheres to the entry port area of the fitment. The bubble will re-enter the lumen when the next drop is dispensed thereby contributing to undesired drop-to-drop volumetric variation contributing to poor user feedback and making manual control difficult.
As can be appreciated, the ability to effect the analysis or test results using very small and precisely measured drop volumes of the fluids involved increases the economic feasibility of such disposable test kits.